Forensic analysis of latent fingermarks by silver-assisted LDI imaging MS on nonconductive surfaces

Silver-assisted laser desorption ionization (AgLDI) imaging mass spectrometry (IMS) has been demonstrated to be a useful technology for fingermark analysis allowing for the detection of several classes of endogenous as well as exogenous compounds. Ideally, in IMS analyses, the fingermarks are deposited under controlled conditions on metallized conductive target slides. However, in forensic investigations, fingermarks are often found on a variety of non-conductive surfaces. A sputtered silver layer renders the target surface conductive, which allows the analyses of insulating surfaces by time-of-flight (TOF) IMS. Ultimately, the major consideration when developing analytical methods for the analysis of latent fingermarks is their capability to be incorporated within forensic standard operational procedures. To demonstrate the potential of AgLDI IMS for forensic applications, fingermarks deposited on non-conductive surfaces commonly found during an investigation, including paper, cardboard, plastic bags and lifting tape were first revealed by the Surete du Quebec using forensic enhancement techniques (FETs) prior to the IMS analyses. Numerous endogenous compounds including fatty acids, cholesterol, squalene, wax esters, triglycerides, as well as several exogenous substances were detected and imaged. Here we show that silver sputtering can provide visual enhancements of fingerprint patterns after FETs procedures through different scenarios in which AgLDI IMS can contribute to forensic investigations.